| Artificial teeth arrangment is a key link in restoration of complete denture. The position of the artificial teeth, the level of occlusal plane and the curvature of occlusal curve directly affect the function, aesthetics of denture and the health of orofacial system. During the developing process of complete denture theory, scholars has presented multiple methods of artificial teeth arrangement. Based on mechanics, maxillary teeth arrangement method suggests that occlusal plane is needed to halve the interridge distance and the back part of occlusal plane is parallel to Comper line. The upper artificial teeth are arranged firstly, then the position of mandibular teeth are determined according to occluding relation. This may reduced the moving space of tongue, and too far distance of lower posterion teeth from mandibular ridge is harmful to the retention and stability of the lower complete denture. Mandibular artificial teeth arrangement method was brought forward according to physiological characteristics of maxilla and mandibule. The absorption of the edentulous ridges makes the shape of maxillary arches change upwards and inside and that of mandibular arches down wards and outside. The fast absorptive speed of mandibular ridge which is more than that of maxillary arches makeothe the retention and stability of lower denture worse than that of upper denture. On the basic of these features, Japanese authors raised the mandibular teeth arrangementmethod in 1950s, According to this method, retromolar pad is used as the reference mark that determine the occlusal plane, and vertical occlusal curve and horizontal occlusal curve are formed by practically measured values. The lower artificial teeth are arranged firstly on the alveolar ridge, then the position of upper artificial teeth is determined, occlusal plane being the maximum upper boundary of lower posterior teeth. In the chinic work, the oral situation of edentulous patients are varied because of the large individual difference, such as cause and time of missing natural teeth, and grantity and speed of the absorption of alveolar ridge. The experienced prosthetics already nolonger use only one teeth arrangement method in the clinic work, but give attention to advantages of different teeth arrangement method in the clinic work, but give attention to advantages of different teeth arrangement method and make use of them synthetically in view of oral condition. This method not only accords with the operative habit of maxillary teeth arrangement method, but also consult the cine tomical properties of retromolar pad and size of tongue to carry out the concrete adjustment for complete denture. In this study, this method was named as synthetic teeth arrangement method for the moment.At present, there were no reports on the gualitative and quantitative analysis comparing the three teeth arrangement methods interiorly. In is an important issue that which method is beneficial for the retention and stability of complete denture, and is in favour of the denture to exert maticatiory officiency and health care of edentulous tissue. Thesystematic investigations were clone by ore discussion group. The ealier X-ray cephalometric study found that: the level of occlusal plane determined by mandibular method is the same as that of natural one on the whole, the level decided by synthetic method approached to the natural occlusal plane, and the level positioned by maxillary method was higher then that of natural teeth apparently; the occlusal plane determined by retromolar pad was more rational and good for the retention and stability of lower denture. The study on the masticatory function releved that: using mandibular teeth arrangement method and synthetic teeth arrangement method to direct the arrangement of artificial teeth can reduce the disadvantage effect on the stability of complete denture as patients masticated. And lead edentulous patients to develop the initiative of masticatory organs, so correspondingly improved masticatiory efficiency. The result suggested that for the edentulous patients whose alveolar ridge showed uneven absorption or mandibular alveolar ridge appeared serious absorption, mandibular teeth arrangement method and synthetic teeth arrangemtn method should be taken into account priorly.An edentulous patient in our hospital who had good alveolar ridges, no distrurbances syndrome of temporomandibular joint, well systematic health candition, and was voluntary to cooperate was selected. Three complete denture according to the three teeth arrangement methods were made for hina, Then CT film was taken, Three three-dimensional finite element model were established based on the CT film, afterwards, theload in term of maximum occlusal force on complete dentures measured practically in olinic was added in negative direction of z-axis, which well stimulated the actual condition, finally, calculation and analysis were undergone. The result showed that the distribution tendancy of Von Miss stress, maximum main stress and minimum main stress of three teeth arrangement method were basically uniform, but there were some difference in the stress value. The stress concentrated on the terminal end of lower posterior alveolar ridge, 2626e part of mandibular ramus, coronoid process, condylar and other site. Under various condition the stress on the posterior area was significantly large than that on anterior area, and the maximum main stress all appeared on the terminal end of lower posterion alveolar ridge. They chiefly focused on the lingually inclined side, and gradually reduced on the buccally in dined side and mesial area. The maximum stress-bearing area was not the alvedar ridge, which was in consistent with traditional definition of main stress-bearing area of dentures. Swoope et al also had similar findings, they stated that the base rotated lingually when the patient masticated, and the maximum stress occurred on the mylohyoid region which was in accordance with the actual chinic situation.Under the condition that each complete denture were all loaded on the whole arches, the maximum main stress values were significantly different for the three teeth arrangement methods. The largest stress valuese appeared when the complete denture was made according to maxillary method, the values for mandibular method took second place,and synthetic method was the last. Parallel to alveolar ridge was an important mark for determining occlusal plane when dentures were made by synthetic method. The ealier x-ray cephalometric measurement also found that the occlusal curve was close to that of natural teeth, for the mandibular inethod and synthetic method, whereas the back part of occlusal curve for maxillary method was away from mandibular alveolar ridge. When occlusal plane was parallel to alveolar ridge, the foree on the alveolar ridge would be distributed evenly, which was favourable for the alveolar ridge would be distributed evenly, which was favourable for the retention of denture, rational distribution of occlusal force, and health care of edentulous tissue. Moreover, when the front level of occlusal plane was significantly lower and back level was upper, the base of lower denture would move towards back edge, so the stress on the mandibular alveolar ridge would increase obviously. The concentration of large stress on some area of alveolar ridge certainly would canse the absorption of bone and be harmful to the protection of tissue.Through the analysis of stress on tissue supporting different complete dentures made according to threes teeth arrangement method, this study enduced such conclusions:1 > The distribution terdancy of stress on edentulous tissue for the complete dentures formed by three teeth arrangement method were coincident on the whole, but stress values were different, value for maxillary method was the largest, then that for mandibular method was... |
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